This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Based on a review of the current literature, we hypothesize the following: H1: Subjects undergoing Roux-en-Y gastric bypass surgery (RYGBS), as compared to morbidly obese controls, will have an increase in baseline (pre-exercise) circulating endothelial progenitor cells (EPC), colony forming units (CFU), and endothelial function 3 months after RYGBS. Additionally, baseline (pre-exercise) inflammatory cytokine concentrations will be reduced. H2: Subjects undergoing RYGBS, as compared to morbidly obese controls, will have an increase in EPC recruitment in response to an acute maximal exercise bout 3 months after RYGBS. H3: The increase in the number of circulating EPCs at baseline and the increased exercise-induced recruitment post-RYGBS will be positively correlated with improved endothelial function and reduced blood concentrations of inflammatory cytokines. Specific Aim1: To evaluate changes in baseline (pre-exercise) EPC number, functionality (CFU), endothelial function, inflammatory cytokines, and cardiorespiratory fitness in morbidly obese individuals 3-months after undergoing gastric bypass surgery and morbidly obese control subjects. Specific Aim2: To evaluate EPC recruitment and changes in endothelial function after a maximal exercise bout in gastric bypass surgery patients before and 3 months after surgery. A non-surgical morbidly obese group will utilized as a control.